Slender steel plates are used in a variety of structural engineering applications because of their high strength-to-weight ratio and post-buckling reserve of strength and stiffness, which is taken into account in ultimate-limit-state design methods and codes of practice. Theoretical procedures for predicting ultimate shear resistance, tf based on tension-field theory and rotating-stress-held theory, are now incorporated in Eurocode 3, Design of Steel Structures (EC3), However, when compared with available test data, theoretical predictions in accordance with the simple post-critical method in EC3 appear inconsistent and unduly conservative. Available test results for the ultimate shear resistance of steel plate girders are reviewed and discussed in this paper. An improved theoretical procedure for predicting the ultimate shear resistance, similar to the simple post-critical method incorporated in EC3 but retaining the rigour of the original rotating-stress-held theory, is presented which shows consistent and significantly improved correlation with the test data.